1. Technical Field
The present disclosure relates to a speaker diaphragm, a speaker including a speaker diaphragm, a device including a speaker, and a method for manufacturing a speaker diaphragm. More specifically, the speaker and the device of the present disclosure relate to a small speaker that is capable of reproducing broadband sound, a video audio device including the speaker (a video display appliance, an audio appliance, an in-ear headphone, a home electrical appliance, and the like), a mobile information processing device (a mobile phone, a smartphone, a tablet PC, an operation terminal, and the like), and a moving device (an automobile, a railroad, and the like).
2. Description of the Related Art
In recent years, video audio devices, so-called audio-visual equipment, are rapidly becoming smaller and their functions are rapidly becoming more complex. This trend is marked especially in mobile phones, smartphones, tablet PC (personal computer) terminals, and the like. Since downsizing and complexity of functions are progressing at the same time, mounted devices are required to be smaller and smaller in size and thickness. A speaker mounted in each appliance is no exception and is required to have a smaller size and smaller thickness while maintaining or improving performance as well as other devices. Therefore, there is a demand for a small speaker that is capable of reproducing sound having a high sound pressure level.
In general, a speaker has a vibrator. The vibrator is vibrated by supplying an electrical signal to a voice coil in a case where the speaker is an electrodynamic speaker or to a piezoelectric element in a case where the speaker is a piezoelectric speaker. This generates a compressional wave in the air. In this way, the speaker reproduces sound. A diaphragm of the speaker is constituted by this vibrator and a suspension that supports an outer peripheral part of the vibrator. The suspension has two functions, i.e., a “supporting” function for supporting the vibrator so that the vibrator is capable of smoothly vibrating and an “antiphase sound suppressing” function for preventing antiphase sound that occurs on the back side of the diaphragm from going around to the front side of the diaphragm and canceling reproduced sound.
In order for a small speaker to reproduce sound of a high sound pressure level, the area of a vibrator needs to be large so that a large volume of air is moved. However, the width of a suspension located on the outer peripheral part of the vibrator needs to be made small in order to increase the area of the vibrator without changing the external shape of the diaphragm. A reduction in the width of the suspension causes an increase in the rigidity of vibrator supporting force. This makes it difficult to reproduce low pitch sound. Since the linearity of the vibrator supporting force deteriorates, the harmonic distortion of reproduced sound increases. Therefore, a suspension of a small speaker is required to have low vibrator supporting rigidity and good linearity of supporting force with respect to the amplitude of the vibrator even if the width of the suspension is small.
In view of this, there is a conventional art for reducing harmonic distortion during reproduction with a speaker by providing slit-like holes in a suspension that supports a vibrator. For example, see Japanese Unexamined Patent Application Publication No. 7-023497. FIG. 14 is a diagram for explaining a diaphragm of a conventional speaker described in Japanese Unexamined Patent Application Publication No. 7-023497.
In FIG. 14, a vibrator 101 is supported by a suspension 102, and the suspension 102 is provided with a plurality of slit-like holes 103. When the vibrator 101 vibrates, stretching contracting force works in the circumferential direction of the edge. This deforms, specifically, widens and narrows the slit-like holes 103 provided in the suspension 102. The deformation allows the suspension 102 to be smoothly deformed in the circumferential direction of the suspension 102. This improves the linearity of the force for supporting the vibrator 101. As a result, it is possible to reduce harmonic distortion of sound reproduced by a speaker using this vibrator 101. Furthermore, easy stretching and contraction in the circumferential direction allows the suspension 102 to be deformed smoothly, thereby reducing the supporting force in a vibration direction of the vibrator 101. This makes it possible to realize a small speaker that is capable of reproducing low pitch sound.
Furthermore, there is a conventional art having a structure such that a plurality of divided sides are connected by a cushion material so as to constitute a suspension (see, for example, Japanese Unexamined Patent Application Publication No. 6-105393). FIGS. 15A and 15B are diagrams for explaining a diaphragm of a conventional speaker described in Japanese Unexamined Patent Application Publication No. 6-105393.
According to the arrangement of FIGS. 15A and 15B, the suspension is constituted by a plurality of divided sides 102a and 102b in order to improve the symmetry of an air exclusion amount of the suspension during vibration of the vibrator 101, and a cushion material 104 is provided over a slit-like hole 103 provided between the divided sides 102a and 102b. This makes it possible to prevent antiphase sound from the back side of the vibrator 101 from going around to the front side of the vibrator 101.